Bats and wind turbines

No form of electrical generation is entirely without unwanted impacts upon plants, animals, and the natural environment. Even the most environmentally appealing options (like solar, wind, and tidal power) have drawbacks. While they are minimal in comparison to the dire consequences of coal, natural gas, or nuclear power, they are real and ought to be acknowledged.

One unfortunate consequence of using wind turbines has recently come to light: the pressure drop near the blades kills bats. This is because the air inside the lungs expands in a low-pressure environment, causing the capillaries surrounding the air chambers to burst.

In the grand scheme of things, bat and bird fatalities produced by strikes and near-strikes on wind turbines are probably not a massive ecological cost. Nonetheless, they demonstrate how challenging it is to operate an industrial, technological society in a manner that is at least somewhat environmentally benign.

ScienceDaily (Aug. 25, 2008) — Power-generating wind turbines have long been recognized as a potentially life-threatening hazard for birds. But at most wind facilities, bats actually die in much greater numbers. Now, researchers reporting in Current Biology, a Cell Press journal, on August 26th think they know why.

Ninety percent of the bats they examined after death showed signs of internal hemorrhaging consistent with trauma from the sudden drop in air pressure (a condition known as barotrauma) at turbine blades. Only about half of the bats showed any evidence of direct contact with the blades.

“Because bats can detect objects with echolocation, they seldom collide with man-made structures,” said Erin Baerwald of the University of Calgary in Canada. “An atmospheric-pressure drop at wind-turbine blades is an undetectable—and potentially unforeseeable—hazard for bats, thus partially explaining the large number of bat fatalities at these specific structure

“The majority of bats killed at wind turbines are migratory bats that roost in trees, including hoary bats, eastern red bats, and silver-haired bats. While little is known about their population sizes, the researchers said, those deaths could have far-reaching consequences.

Bats typically live for many years, in some cases reaching ages of 30 or more. Most also have just one or two pups at a time, and not necessarily every year. “Slow reproductive rates can limit a population’s ability to recover from crashes and thereby increase the risk of endangerment or extinction,” said Robert Barclay, also at the University of Calgary, noting that migrating animals tend to be more vulnerable as it is.

All three species of migratory bats killed by wind turbines fly at night, eating thousands of insects—including many crop pests—per day as they go. Therefore, bat losses in one area could have very real effects on ecosystems miles away, along the bats’ migration routes.”

Texas regulators have approved a $4.93 billion wind-power transmission project, providing a major lift to the development of wind energy in the state.

The planned web of transmission lines will carry electricity from remote western parts of the state to major population centers like Dallas, Houston, Austin and San Antonio. The lines can handle 18,500 megawatts of power, enough for 3.7 million homes on a hot day when air-conditioners are running.

The project will ease a bottleneck that has become a major obstacle to development of the wind-rich Texas Panhandle and other areas suitable for wind generation.

A more efficient generator could convert more of the wind’s energy into electricity.

ExRo Technologies, a startup based in Vancouver, BC, has developed a new kind of generator that’s well suited to harvesting energy from wind. It could lower the cost of wind turbines while increasing their power output by 50 percent.

The new generator runs efficiently over a wider range of conditions than conventional generators do. When the shaft running through an ordinary generator is turning at the optimal rate, more than 90 percent of its energy can be converted into electricity. But if it speeds up or slows down, the generator’s efficiency drops dramatically. This isn’t a problem in conventional power plants, where the turbines turn at a steady rate, fed by a constant supply of energy from coal or some other fuel. But wind speed can vary wildly. Turbine blades that change pitch to catch more or less wind can help, as can transmissions that mediate between the spinning blades and the generator shaft. But transmissions add both manufacturing and maintenance costs, and there’s a limit to how much changing the blade angle can compensate for changing winds.

Do windmills kill “huge numbers” of birds? Wind farms recently got adverse publicity from Norway, where the wind turbines on Smola, a set of islands off the north-west coast, killed 9 white-tailed eagles in 10 months. I share the concern of BirdLife International for the welfare of rare birds. But I think, as always, it’s important to do the numbers. It’s been estimated that 30 000 birds per year are killed by wind turbines in Denmark, where windmills generate 9% of the electricity. Horror! Ban windmills! We also learn, moreover, that traffic kills one million birds per year in Denmark. Thirty-times-greater horror! Thirty-times-greater incentive to ban cars! And in Britain, 55 million birds per year are killed by cats.